1. Field of the Invention
The present invention concerns a method for automatic position determination in at least one spatial direction of acquisition devices (in particular local coils) that are movable move relative to a magnetic resonance tomography scanner. The invention also concerns a corresponding control device, a magnetic resonance system and a computer program product and an electronically readable data medium.
2. Description of the Prior Art
Modern magnetic resonance systems normally operate with a number of different antennas (also called coils herein) for emission of radio-frequency pulses for nuclear magnetic resonance excitation and/or for acquisition of the excited magnetic resonance signals. A magnetic resonance system normally has a larger whole-body coil (body coil) permanently installed in the apparatus. The whole-body coil is typically arranged cylindrically around the patient acceptance space (for example with a structure known as a birdcage structure) in which the patient is supported on a recumbent panel or table during a measurement. Furthermore, one or more acquisition devices (i.e. small coils or called local coils or surface coils) are frequently used in a tomography apparatus. The local coils serve to acquire detailed images of body parts or organs of a patient that are located relatively near to the body surface. For this purpose the local coils are applied directly at the location of the patient at which the region to be examined is located. In the use of such local coils transmission occurs with the whole-body coil (as a transmission coil) and the excited magnetic resonance signals are acquired with the local coils (as acquisition coils).
For a magnetic resonance examination it is important to know the exact position of the employed local coils relative to the patient support (and thus relative to the patient). In principle it is possible to manually measure the position of the coils with the aid of rulers, scales, markings, etc. on the patient support when it is moved out from the magnetic resonance system. Particularly when a number of local coils are used or when coil arrays composed of multiple coils are used, such a measurement is very complicated and additionally entails the risk that the measured positions are associated with the wrong coils. It is therefore simpler and safer to automatically determine the position of the local coils in the framework of a magnetic resonance measurement.
However, one acquisition channel of the magnetic resonance system per local coil is required in order to automatically determine the position of the local coils in the framework of a magnetic resonance measurement. Since the number of the acquisition channels is limited for cost reasons, the number of the local coils to be measured frequently exceeds the number of the acquisition channels.